1. Field
Apparatuses and methods consistent with exemplary embodiments relate to optical image shutters and methods of manufacturing optical image shutters, and more particularly, to optical image shutters having transparent electro-optical crystal formed on transparent amorphous substrates.
2. Description of the Related Art
Optical image shutters transmit or block an optical image containing information according to a control signal. Optical shutters are essential optical modules widely used in image pickup devices, such as cameras, and display devices, such as liquid crystal displays (LCDs).
Optical shutters may be technically classified into a mechanical shutter used in a camera or the like, a liquid crystal shutter used in an LCD, a digital micromirror device used in a projection display device, a micro-electro-mechanical system (MEMS)-based spatial light modulator such as a grating light-valve, an image intensifier used in a laser radar (LADAR) or a three-dimensional (3D) camera, and a semiconductor-based optical shutter.
In terms of working principles and shutter speeds, a mechanical shutter drives an aperture by using an electro-magnetic motor and has a shutter time on the order of 1 millisecond (ms). A liquid crystal shutter is driven by the rotation of liquid crystal molecules and has a shutter time of several milliseconds. A MEMS-based spatial light modulator drives a fine structure with an electrostatic force and has an operation time of tens of microseconds (μs). An intensifier used in a 3D camera and a semiconductor-based optical shutter are driven by photoelectric conversion occurring in a semiconductor and have a shutter time of several nanoseconds (ns).
Much research into obtaining distance information of a subject by using a LADAR or a 3D camera has been recently conducted. To obtain the distance information, light having a specific wavelength (for example, a near infrared ray having a wavelength of 860 nm) is projected onto the subject by using an LED or a laser diode (LD), a light image reflected from the subject is (shuttered), an image is obtained via an imaging device, and a series of processing is performed on the image. In this regard, a fast shutter opening and closing time of about tens of ns is used to exactly identify a light traveling time to determine a distance. An image shutter, such as the image intensifier or the semiconductor-based optical shutter stated above, provides a fast shutter opening and closing time.
The image intensifier is an expensive piece of equipment requiring a high operating voltage and vacuum packaging. The semiconductor-based optical shutter includes a light absorber using a multi-quantum well structure based on a III-V group semiconductor, such as GaAs, a combination of an opto-electric converter (for example, a photodiode), and an electro-optical converter (for example, an LED), etc. The semiconductor-based optical shutter is manufactured using a GaAs substrate during a semiconductor manufacturing process.
In addition to the light shutters described above, another kind of light shutter relies on an electro-optical effect in which a refractive index varies according to an electric field applied thereon. Since the light shutter relying on the electro-optical effect described above has a response speed corresponding to several tens of GHz, it may be used as a waveguide in ultra-speed optical communication. Examples of the light shutter relying on the electro-optical effect described above include a Kerr cell using the Kerr effect and a Pockel cell using the Pockel effect. Kerr cells and Pockel cells relying on the electro-optical effect described above often use a bulk electro-optical crystal that requires a driving voltage of thousands of volts in order to obtain a desired effect. It has recently been proposed that a light shutter that operates at a low voltage can be created by forming a thin film using an electric-optic material. In this regard, a technology for crystallizing the electro-optical material as a thin film on an amorphous substrate such as glass is at issue.